RFID has been a key technology for short range wireless auto identification. It has been implemented in many recent technologies such as contact-less smart cards, access control, wireless sensing and information collection, industrial automation, ticketing, public transportation, automatic toll collection, animal and product tracking, and medical applications.
Referring to FIG. 1, a typical RFID system 100 consists of two major blocks: an interrogator, known as RFID reader 104, and a remote unit, known as RFID tag 101. The tag has a unique identification code incorporated into the ID circuit 102 and this code becomes associated with the object to which the RFID tag is attached. The RFID reader 104 normally has a transmitter/receiver unit which transmits a signal to and receives a response from the RFID tag. The RFID tag will have an antenna 103 and the RFID reader will have an antenna 107. Unlike barcode technology, an RFID tag can convey more extensive information about the object. The reader sends an interrogation signal and the tag responds with the information stored in it. A RFID system does not require line of sight, and information can be read from comparatively longer distances than bar code scanners. Moreover, multiple tags can be read simultaneously.
RFID tags can be classified as active, reader powered tags (inductive coupling) and fully passive tags. Active tags require power source to operate, therefore are limited by their battery life. Reader powered tags operate by inductive coupling; therefore they are limited by read distance. On the other hand, passive tags consist primarily of an antenna and an ID circuit. They do not require any power supply and work by responding to reader interrogation by changing certain parameters of the interrogation signal. Passive tags tend to be more limited by their read distance and the amount of information that they can convey.